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Airwaves: August 5, 2011

Can You hear Me Now?

There’s been a lot of talk over the past few years regarding interference on the AM and FM bands. Actually, the discussion goes back decades, to the very start of experimental radio broadcasts -- one of the reasons Edwin Armstrong invented FM is that he couldn’t stand the interference he heard on his (and others) first radio invention, AM -- but the topic has been getting more traction ever since the FCC allowed digital HD Radio broadcasts.

HD Radio itself can cause problems, especially on the AM band where stations are very close together compared with FM and television. This is due to the digital broadcasts surpassing the bandwidth of regular music or talk programming, and radios sometimes picking up the digital “hash.” On AM it is like hearing white noise over weak stations, on FM it theoretically can cause FM radios to become “confused” and make weak or distant stations simply disappear.

But is HD Radio getting too much of the blame? As I said, interference has been a problem since the beginning of radio. First it was natural -- lightening, for example -- and eventually man-made. And it is definitely a problem, especially when you consider that early 50-watt AM stations could be heard across the country in the 1920s ... 50 watts would barely get you across the street today.

So what’s the problem? LED traffic lights? Power lines? Neon signs? Yes, to a point. All of those have the potential to hurt reception of both AM and FM broadcasts. But it turns out that most reception problems are closer to home. Your home, and what you have inside.

The cell phone charger you keep plugged in? Noisy interference unit. Your DVD player? Same thing. Your cable box and big-screen television? You guessed it. And while all of these items have been long known to cause problems directly to AM stations, Steve Johnson, engineer for Wisconsin Public Radio found that they cause problems for FM. Not just analog FM, by the way, HD FM is affected too. SO HD isn’t necessarily to blame for reception troubles, at least when it comes to FM.

Johnson took measurements throughout homes in the Wisconsin area, sparked by an increase of 37 percent of the number of listener complaints regarding decreased reception of the stations he oversees. He found that interference indoors was higher than outdoors, even if it was just outside the house. It didn’t matter if it was an urban apartment, an office, or a suburban house, the result was the same: greatly increased interference -- as much as 20 to 30 dB -- and lessened reception indoors.

He found that recently manufactured plug-in “wall-wart” power supplies, as found powering small electronics, were the worst offenders. Some HD televisions and DVD players were bad as well, something Johnson feels may also be power-supply related. Computers, and in fact almost any electronic device, have the potential to wreak havoc with radio reception on AM, FM and even television. Sometimes it was a manufacturing problem -- shielding missing from a battery charger built in China, other times it is the actual circuit design.

Long-term, Johnson says that broadcasters must insist that products do not cause interference ... something that already is a requirement of the FCC but is obviously not necessarily enforced. Short-term, you may have to move your radio (often a few feet or a small turn will improve things noticeably) or install an outdoor antenna if you are having problems picking up your favorite station.

HD Update

Mexico has decided to allow the HD Radio system to be used by broadcasters throughout the country; previously they had allowed such broadcasts by stations within 200 miles of the United States border. It is not the digital broadcast standard, however, so it is possible that another system could be introduced in the future.


Copyright © 2011 Richard Wagoner and Los Angeles Newspaper Group.

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